It has been shown in the prior art that desired position isomers such as the ortho isomer may be obtained by adding .pi.-donating compounds such as polynuclear aromatic compounds such as naphthalene and anthracene to a reaction mixture. Likewise, the prior art has also disclosed that when anisole is subjected to an acetoxylation process, the ortho to para ratio is about 2:1 at low conversions of from 5% to 10% and increases to about 4:1 at a 25% conversion of the anisole. The usual prior art systems which were employed in the acetoxylation of aromatic compounds utilized non-emulsion conditions. This type of reaction required a relatively high operating voltage in the range of about 20 volts in order to obtain a reasonable current density. Therefore, the desired products were obtained at a high cost of power per pound of product.
In many instances, it has been found that the desired position isomer comprises the para isomer and therefore it has been unexpectedly discovered that by effecting the electrochemical oxidation of alkoxy-substituted aromatic compounds in the presence of an acid of the type hereinafter set forth in greater detail as well as salts thereof and also in the presence of a phase transfer agent, it is possible to reverse the ortho:para ratio which was present in reactions involving methods set forth in the prior art and therefore make it possible to obtain a greater amount of the desired para isomer. That is, by using bulky acids and emulsion conditions it is possible to carry out the electrochemical oxidation of an aromatic compound to a relatively high conversion rate without significantly losing the selectivity of desired products.
This invention relates to a process for the electrochemical oxidation of alkoxy-substituted aromatic compounds. More specifically, the invention is concerned with a process for obtaining improved yields of the desired position isomer during the electrochemical oxidation of alkoxy-substituted aromatic compounds.
Certain chemical compounds, and especially those which contain two substituents in a position para to each other, comprise desired reaction products which are useful in the chemical field. For example, hydroxyanisole may be synthesized electrochemically from anisole. The reaction is carried out in an electrochemical cell so that the desired product is obtained at the anode, said reaction involving the anodic oxidation of anisole in the presence of a nucleophile such as acetate ions which lead to acetoxylation in the ortho and para positions. The para isomer of the reaction constitutes a valuable intermediate inasmuch as the acetoxylated product in which the acetoxy substituent is in a para position is an intermediate for the production of p-hydroxyanisole, this compound being the precursor of t-butylhydroxyanisole which is an antioxidant useful in preventing the oxidation of edible fats and oils. In addition to being admixed with these fats and oils it is also used in food packaging, the wrappings for the foods containing this compound.
It is therefore an object of the present invention to provide a process for the electrochemical oxidation of alkoxy-substituted aromatic compounds.
A further object of this invention is to provide a method for obtaining improved yields of desired position isomers which result from the electrochemical oxidation of alkoxy-substituted aromatic compounds.
In one aspect an embodiment of this invention resides in a process for the electrochemical oxidation of an alkoxy-substituted aromatic compound which comprises treating said compound at reaction conditions with an acid having the formula: ##STR1## in which at least 2 R's are alkyl groups containing from 1 to about 10 carbon atoms and the remaining R is hydrogen or an alkyl group containing from 1 to about 10 carbon atoms and an alkali or alkaline earth metal salt of such an acid and a phase transfer agent comprising a symmetrical or asymmetrical tetraalkylnitrogen or phosphorus-based salt containing from 1 to about 20 carbon atoms in the alkyl chain, in an electrochemical cell maintained at a voltage in the range of from about 2 to about 20 volts and a current density in the range of from about 20 to about 200 milliamperes/square centimeter, and recovering the resultant acetoxylated alkoxy-substituted aromatic compound.
A specific embodiment of this invention is found in a process for the electrochemical oxidation of an alkoxy-substituted aromatic compound which comprises treating anisole with pivalic acid in the presence of tetraethylammonium sulfate in an electrochemical cell utilizing electrical energy conditions which include a voltage in the range of from about 2 to about 20 volts and a current density in the range of from about 20 to about 200 milliamperes per square centimeter (ma/cm.sup.2) at ambient temperature and atmospheric pressures, and recovering the resultant p-pivaloxyanisole.
Other objects and embodiments will be found in the following further detailed description of the present invention.